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133 lines
2.7 KiB
Markdown
133 lines
2.7 KiB
Markdown
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class: title
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# Copying files during the build
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---
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## Objectives
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So far, we have installed things in our container images
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by downloading packages.
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We can also copy files from the *build context* to the
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container that we are building.
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Remember: the *build context* is the directory containing
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the Dockerfile.
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In this chapter, we will learn a new Dockerfile keyword: `COPY`.
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---
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## Build some C code
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We want to build a container that compiles a basic "Hello world" program in C.
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Here is the program, `hello.c`:
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```bash
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int main () {
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puts("Hello, world!");
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return 0;
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}
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```
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Let's create a new directory, and put this file in there.
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Then we will write the Dockerfile.
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---
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## The Dockerfile
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On Debian and Ubuntu, the package `build-essential` will get us a compiler.
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When installing it, don't forget to specify the `-y` flag, otherwise the build will fail (since the build cannot be interactive).
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Then we will use `COPY` to place the source file into the container.
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```bash
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FROM ubuntu
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RUN apt-get update
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RUN apt-get install -y build-essential
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COPY hello.c /
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RUN make hello
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CMD /hello
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```
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Create this Dockerfile.
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---
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## Testing our C program
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* Create `hello.c` and `Dockerfile` in the same directory.
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* Run `docker build -t hello .` in this directory.
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* Run `docker run hello`, you should see `Hello, world!`.
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Success!
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---
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## `COPY` and the build cache
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* Run the build again.
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* Now, modify `hello.c` and run the build again.
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* Docker can cache steps involving `COPY`.
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* Those steps will not be executed again if the files haven't been changed.
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---
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## Details
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* We can `COPY` whole directories recursively
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* It is possible to do e.g. `COPY . .`
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(but it might require some extra precautions to avoid copying too much)
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* In older Dockerfiles, you might see the `ADD` command; consider it deprecated
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(it is similar to `COPY` but can automatically extract archives)
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* If we really wanted to compile C code in a container, we would:
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* place it in a different directory, with the `WORKDIR` instruction
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* even better, use the `gcc` official image
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---
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class: extra-details
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## `.dockerignore`
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- We can create a file named `.dockerignore`
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(at the top-level of the build context)
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- It can contain file names and globs to ignore
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- They won't be sent to the builder
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(and won't end up in the resulting image)
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- See the [documentation] for the little details
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(exceptions can be made with `!`, multiple directory levels with `**`...)
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[documentation]: https://docs.docker.com/engine/reference/builder/#dockerignore-file
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???
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:EN:- Leveraging the build cache for faster builds
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:FR:- Tirer parti du cache afin d'optimiser la vitesse de *build*
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